MulticastReceiver.java

package UdpMulticastHttpExamples;

import java.io.*;
import java.net.*;

/**
 *
 * @author mcgredo
 */
public class MulticastReceiver {

    public static final String MULTICAST_ADDRESS = "239.1.2.15";
    public static final int     DESTINATION_PORT = 1718;
    /** How many routers can be crossed */
    public static final int TTL = 10; 
    
    public static void main(String[] args) 
    {
        try
        {
            System.out.println("MulticastReceiver started...");
        
            // This is a java/IPv6 problem. You should also add it to the
            // arguments used to start the app, eg -Djava.net.preferIPv4Stack=true
            // set in the "run" section of preferences. Also, typically
            // netbeans must be restarted after these settings.
            // https://stackoverflow.com/questions/18747134/getting-cant-assign-requested-address-java-net-socketexception-using-ehcache
            System.setProperty("java.net.preferIPv4Stack", "true");
            
            MulticastSocket multicastSocket = new MulticastSocket(DESTINATION_PORT);
            multicastSocket.setTimeToLive(TTL);
            InetAddress multicastAddress = InetAddress.getByName(MULTICAST_ADDRESS);
            // Join group useful on receiving side
            multicastSocket.joinGroup(multicastAddress);
            // You can join multiple groups here
            System.out.println("Multicast address/port: " + multicastAddress.getHostAddress() + "/" + DESTINATION_PORT);
            System.out.println("Multicast packets received log:");
            
            int count = 0; // initialize
            
            while(true)
            {
                byte[] packetArray = new byte[1500]; // note use of typical MTU value
                DatagramPacket packet = new DatagramPacket(packetArray, packetArray.length);
                
                multicastSocket.receive(packet);
                count++;
                
                ByteArrayInputStream bais = new ByteArrayInputStream(packet.getData());
                DataInputStream dis = new DataInputStream(bais);
				String firstCharacters = new String();
				char   nextChar  = ' ';
				while (nextChar != ';') // read and build string until terminator ; found
				{
					nextChar = dis.readChar();
					firstCharacters += nextChar;
				}
				if (firstCharacters.equals("quit;"))
				{
					System.out.println("Received \"quit;\" sentinel");
					break; // exit out of reading loop
				}
				int   index       = dis.readInt();
                float firstFloat  = dis.readFloat();
                float secondFloat = dis.readFloat();
                
				if (count < 10) System.out.print(" "); // prettier output formatting
                System.out.print(count + ". \"" + firstCharacters + "\" "); // wrap string in quote marks
                System.out.println("index=" + index + ", firstFloat=" + firstFloat + " secondFloat=" + secondFloat);
            }
            System.out.println("MulticastReceiver loop complete.");
        }
        catch(IOException e)
        {
            System.out.println("Problem with MulticastReceiver, see exception trace:");
            System.out.println(e);
        }
		finally // clean up after exit condition
		{
			// socket/database/completion cleanup code can go here, if needed.
            System.out.println("MulticastReceiver finally block, complete.");
		}
    }
}